Up to recently, in order to determine the position of an object, such as a writing material, on the surface on which data is recorded or data is not recorded, a variety of methods have been tried. In particular, in relation to a position determination method using an electronic pen, apparatuses for determining a 2-dimensional or a 3-dimensional position in order to input graphic data such as written letters, symbols, and pictures, have been introduced. According to a method of converting position information sensed by a data sensing unit into coordinates, these apparatuses determine an absolute position of a sensing unit on a surface on which data is recorded.
In order to input the written data, a sensing unit, such as a tablet for writing, can be used. Most of 2-dimensional apparatuses are operated by contacts between the writing tablet and the sensing unit.
Generally there are two relations between the sensing unit and the tablet: a passive sensing unit with an active tablet and an active sensing unit with a passive tablet.
In the method of the passive sensing unit with the active tablet, the active tablet is large, heavy, and difficult to carry, and in addition, very expensive. Furthermore, it is difficult to manufacture the active tablet, and due to its complicated electromechanical structure, errors and other incorrect operations may occur easily.
Meanwhile, in the method of the active sensing unit with the passive tablet, the sensing apparatus and a processing apparatus are generally separated, and in addition, coding of the tablet is required such that the use of the tablet is inconvenient. Furthermore, an unexpected error may occur in the process that a signal transmitted by the sensing unit is returning from the tablet to a receiver.
Accordingly, since both the passive sensing unit with the active tablet and the active sensing unit with the passive tablet have the problems described above, careful adjustment of the interface should be performed in order to use the apparatuses as if a user wrote a letter with an ordinary pen. However, the amount of information and accuracy provided by these methods are limited. Also, development of an apparatus capable of processing collectively the information such as the movement, rotation of a sensing unit, the use angle and writing speed of the sensing unit about the tablet has been needed.
To solve these problems, an apparatus enabling easy determination of an absolute position of a sensing unit has been suggested. The apparatus includes a data recording surface on which a coding pattern is provided; a sensor capable of sensing the coding pattern; and a processor capable of determining a current position of the sensor based on a sensed coding pattern. In the operation of this apparatus, if the user writes letters or draws a picture on the data recording surface, the data is displayed on the computer monitor.
There are a variety of methods for coding by using this apparatus, and an example is as the following.
As shown in FIG. 1, according to the method, a symbol is made to be a pattern for coding a position. Each signal is composed of three concentric circles. The outermost circle drawn outermost indicates an X coordinate, and the middle circle indicates a Y coordinate. Each of the outermost circle and the middle circle is divided into 16 parts, each of which indicates a different code according to whether the part is filled or empty. This means that each pair of coordinates is coded by a complicated sign having a predetermined appearance.
As another method, X, Y coordinates can be coded by using check patterns. Here, the method of coding positions is the same as that using the concentric circles.
These known patterns are composed of complicated signs, and the smaller and finer these signs are, the more difficult the implementation of the patterns on a data recording surface becomes. When the resolution of the sensing unit is not high, a fine pattern cannot be recognized accurately and it is highly probable that an error in recognition of a position occurs. Meanwhile, if the signs of the pattern are made to be simple and coarsened, identical microcodes of identical patterns at different positions on the data recording surface may cause duplication. Accordingly, the accuracy for determining an absolute position is lowered and it is difficult for the position sensing unit to sense an accurate position.
Meanwhile, as shown in FIG. 2, there is a coordinate recognition method by a position-coding pattern in which a point is marked on one of 4 positions (left, right, top, and bottom) around each intersection of a plurality of virtual horizontal axes and vertical axes. More specifically, a point is marked on any one of the four places around each intersection of all axes perpendicular to each other and having narrow intervals. Each arrangement with respect to the positions of these points are made to be different to each other and allocated a unique microcode. By sensing these arrangements, a current position of a sensing unit is determined.
However, if patterns are implemented in this method, the number of cases arranging one point around an intersection is limited to 4, and the types of microcodes allocated to the limited number of neighboring points cannot be diversified. That is, due to duplication of identical microcodes an error in recognition of a position can occur. In order to solve this problem, more points should be arranged in a unit area, and the size of each point should be reduced appropriate to the area. This means that when a microcode is allocated to neighboring points, the microcode should be expressed by a more number of points. Accordingly, a pattern recording medium should be printed by a very fine printing or output apparatus, and a sensing unit should have a very high resolution in order to sense each point on the axes having narrow intervals. As a result, in the process of sensing a code, an error in recognition of the position of the sensing unit may still occur.
Meanwhile, instead of obtaining an intersection from horizontal axes and vertical axes perpendicular to each other, virtual lines may be placed to cross each other to make a 120 degree angle, or to make a honeycomb. Then, a point can be disposed around an intersection corresponding to a corner. However, in this case, the number of cases of disposing one point is also limited to 3 or 4, and the problem described above arises.
In addition to disposing points to the left, and right on the horizontal axis, and above and below on the vertical axis of an intersection as in FIG. 2, by further disposing a point to the left below, to the right below, to the left above, and to the right above an intersection, the number of cases of arrangements can be increased. However, in this case the sensing unit should sense a fine change of the position of a point, and therefore the sensing unit, that is, an image system, having a very high resolution is required.